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Core Java - Interview Questions and Answers for 'Static' - 63 question(s) found - Order By Newest

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  Q1. What do you mean by "Java is a statically typed language" ?Core Java
Ans. It means that the type of variables are checked at compile time in Java.The main advantage here is that all kinds of checking can be done by the compiler and hence will reduce bugs.

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 Q2. How can we run a java program without making any object?Core Java
Ans. By putting code within static method. With Java 6 and earlier versions, even static block can be used.

  Sample Code for static block

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 Q3. What are the advantages and disadvantages of static variables and static methods ?Core Java
Ans. Advantages

Can do meta object operations ( like validating something before creating objects , keep count of number of objects )

Can do operations which have nothing to do with objects but still you want them to be tied to Class.

Disadvantages

Commonly used to static variables sometime leads to problems due to access by different objects.

Are not tied to objects so doesn't reflect pure Object Oriented approach.

Needs to be synchronized so as to avoid update conflicts by mutiple objects and threads.

Some limitation in testing as not all frameworks have facility to mock them. Powermock has but Mockito doesnt

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 Q4. Difference between Static and Singleton Class ?Core Java
Ans. 1. Static class is a class which cannot be instantiated and all its members are static whereas Singleton is the class that only permit creation of single object and then the object is reused.

2. As there is no object in Static class, it cannot participate in runtime Polymorphism.

3. As Static class doesnt allow creating objects and hence it cannot be serialized.

4. Static class body is initialized eagerly at application load time whereas Singleton object can be initiated eagerly using static blocks or lazily on first need.

5. Its not recommended to use pure static class as it fails to use many OOPs concepts.

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 Q5. Can we declare static variables as transient ?Core Java
Ans. It's weird that compiler doesn't complain if we declare transient with static variable because it makes no sense. At least a warning message saying "transient is useless in this situation" would have helped with code cleaning.

Static variables are never serialized and transient is an indication that the specified variable shouldn't be serialized so its kind of double enforcement not to serialize.

It could be that as it makes no different to the variable behavior and hence using both keywords with a variable are permitted.

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 Q6. What are concepts introduced with Java 5 ?Core Java
Ans. Generics , Enums , Autoboxing , Annotations and Static Import.

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 Q7. Which of the following can be marked static ?

a. Methods , Variables and Initialization Blocks.
b. Methods , Variables , Initialization Blocks and Outer Classes and nested Classes.
c. Methods , Variables , Initialization Blocks and Outer Classes.
d. Methods , Variables , Initialization Blocks and nested Classes
Core Java
Ans. Methods , Variables , Initialization Blocks and nested Classes

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 Q8. What is the difference between the following two code lines ?

1. new OuterClass().new InnerClass();

2. new OuterClass.InnerClass();
Core Java
Ans. In first case we are trying to initialize Inner class object using the instance of Outer Class whereas in second case we are trying to initialize the Inner class object directly using the Outer class name.

In second case , Inner class is "static inner class" as we cannot access "non static inner class" using Classname alone.

In first case, the inner class could be either "static inner class" or "non static inner class".

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 Q9. Can we access instance variables within static methods ?Core Java
Ans. Yes.we cannot access them directly but we can access them using object reference.Static methods belong to a class and not objects whereas non static members are tied to an instance. Accessing instance variables without the instance handler would mean an ambiguity regarding which instance the method is referring to and hence its prohibited.

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 Q10. When are static variables loaded in memory ?Core Java
Ans. They are loaded at runtime when the respective Class is loaded.

  Sample Code for static variable

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 Q11. Can we serialize static variables ?Core Java
Ans. No. Only Object and its members are serialized. Static variables are shared variables and doesn't correspond to a specific object.

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 Q12. Similarity and Difference between static block and static method ?Core Java
Ans. Both belong to the class as a whole and not to the individual objects. Static methods are explicitly called for execution whereas Static block gets executed when the Class gets loaded by the JVM.

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 Q13. In which cases , moving methods to utility class could be useful ?Core Java
Ans. It could be worthy to move a method to util class if the method needs to be shared, doesn't require polymorphic behavior and need not be overridden in special cases.

Don't belong to one group through is-a relationship ( You can share through parent class method )

Don't implement a specific interface ( java 8 default methods )

Doesn't involve complex computing as you will be loosing the benefit of object state with just static method.

Doesn't require polymorphic behavior as static methods don't participate in runtime polymorphism.

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 Q14. Can we override static methods ? Why ?Core Java
Ans. No.

Static methods belong to the class and not the objects. They belong to the class and hence doesn't fit properly for the polymorphic behavior.

A static method is not associated with any instance of a class so the concept of overriding for runtime polymorphism using static methods is not applicable.

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 Q15. What is a Static import ?Core Java
Ans. By static import , we can access the static members of a class directly without prefixing it with the class name.

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 Q16. How can we create objects if we make the constructor private ?Core Java
Ans. We can do so through a static public member method or static block.

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 Q17. Difference between nested and inner classes ?
Ans. Inner class is a type of nested class.

Inner classes are non static nested classes i.e the one that are associated with the instance of outer class.

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 Q18. Difference between static vs. dynamic class loading?Core Java
Ans. static loading - Classes are statically loaded with Java new operator.

dynamic class loading - Dynamic loading is a technique for programmatically invoking the functions of a class loader at run time.

Class.forName (Test className);

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 Q19. Is it possible to compile and run a Java program without writing main( ) method?
Ans. Yes, it is possible by using a static block in the Java program.

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 Q20. Will the following program display ""Buggy Bread"" ?

class Test{
   static void display(){
      System.out.println(""Buggy Bread"");
   }
}

class Demo{
   public static void main(String... args){
      Test t = null;
      t.display();
   }
}
Core Java
Ans.  Yes. static method is not accessed by the instance of class. Either you call it by the class name or the reference.

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 Q21. Which of the following syntax is correct ?import static java.lang.System.*;or static import java.lang.System.*;Core Java
Ans. import static java.lang.System.*;

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 Q22. Can we use static method definitions in Interfaces ?Core Java
Ans. Yes, Effective Java 8.

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 Q23. Why can't we use this in static context ?Core Java
Ans. Static methods can be called using instance references wherein this would have made sense but static method can also be called using Class name wherein this would mean nothing and hence forbidden.

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 Q24. Which of the following cannot be marked static ?

a. Constructors , Classes ( Outer ) , Classes ( nested ), Interfaces , Local variables , Inner Class methods and instance variables.
b. Constructors , Classes ( Outer ) , Interfaces , Local variables , Class variables , Class Methods , Inner Class methods and instance variables.
c. Constructors , Classes ( Outer ) , Interfaces , Local variables , Inner Class methods and instance variables.
d. Constructors , Classes ( Outer ) , Classes (Nested), Interfaces , Local variables , Inner Class methods and instance variables
Ans. Constructors , Classes ( Outer ) , Interfaces , Local variables , Inner Class methods and instance variables.

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 Q25. What is the use of static keyword in Java ?Core Java
Ans. static keyword is used to specify that the respective programming construct ( method , variable ) belongs to the class and not to its instance and is supposed to be shared by all instances of the class.

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 Q26. How can we ensure thread safety in static method ?Core Java
Ans. By using synchronized static method or synchronized block

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 Q27. Can static method access instance variables ?Core Java
Ans. Though Static methods cannot access the instance variables directly, They can access them using instance handler.

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 Q28. Does java allow overriding static methods ?Core Java
Ans. No. Static methods belong to the class and not the objects. They belong to the class and hence doesn't fit properly for the polymorphic behavior.

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  Q29. Explain static blocks in Java ?Core Java
Ans. A static initialization block is a normal block of code enclosed in braces, { }, and preceded by the static keyword. Here is an example:

static {
// whatever code is needed for initialization goes here
}

A class can have any number of static initialization blocks, and they can appear anywhere in the class body. The runtime system guarantees that static initialization blocks are called in the order that they appear in the source code.

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 Q30. Explain Static nested Classes ?
Ans. The accessibility (public, protected, etc.) of the static nested class is defined by the outer class.

A static nested class is not an inner class, it's a top-level nested class.

The name of the static nested class is expressed with OuterClassName.NestedClassName syntax.

When you define an inner nested class (or interface) inside an interface, the nested class is declared implicitly public and static.

Static nested classes can be declared abstract or final.

Static nested classes can extend another class or it can be used as a base class.

Static nested classes can have static members.

Static nested classes can access the members of the outer class (only static members, obviously).

The outer class can also access the members (even private members) of the nested class through an object of nested class. If you don't declare an instance of the nested class, the outer class cannot access nested class elements directly.

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